The present invention relates to a magnetic resonance imaging (MRI) system in which a measuring technique utilizing the magnetic resonance (MR) phenomenon is adopted in a computed tomography (CT) technique and, more particularly, to a fast reconstruction technique for obtaining a reconstructed image in a short time in a system in which a back projection method is adopted in image reconstruction.
In such an MRI system, the MR phenomenon occurs in an object to be examined, and a magnetic wave which is excited by the MR phenomenon is detected as an MR signal. In accordance with this MR signal, projection data in which resonance data of specific nucleus is projected on a specific slice of the object to be examined can be obtained in many directions. These projection data are subjected to image reconstruction processing, and image data representing at least one of a spin density of the specific nucleus and a relaxation time constant can be obtained. In this manner, a technique for obtaining the image data representing at least one of the spin density and the relaxation time constant is called magnetic resonance imaging (MRI). Since the MRI system can be effectively used for medical diagnosis, it is beginning to be used for medical use.
In this MRI system when the back projection method is adoped in image reconstruction, convolution calculation, back projection image reconstruction calculation and the like are needed. These processings become a large load to a host central processing unit (CPU), and time necessary for finally obtaining the reconstructed image cannot be ignored. A fast reconstructing unit (FRU) which is used in an X-ray computed tomographic system (referred to as XCT system hereafter) cannot be used in the MRI system because of a difference between projection principles of the XCT system and the MRI system. Thus, development of the FRU for the MRI system has been recently demanded. Furthermore, in order to popularize the MRI system, cost for realizing the FRU must be minimized.